29 C.F.R. § 102.29
Any person desiring to intervene in any proceeding must file a motion in writing or, if made at the hearing, may move orally on the record, stating the grounds upon which such person claims an interest. Prior to the hearing, such a motion must be filed with the Regional Director issuing the complaint; during the hearing, such motion must be made to the Administrative Law Judge. Immediately upon filing a written motion, the moving party must serve a copy on the other parties. The Regional Director will rule upon all such motions filed prior to the hearing, and will serve a copy of the rulings on the other parties, or may refer the motion to the Administrative Law Judge for ruling. The Administrative Law Judge will rule upon all such motions made at the hearing or referred to the Judge by the Regional Director, in the manner set forth in § 102.25 . The Regional Director or the Administrative Law Judge, as the case may be, may, by order, permit intervention in person, or by counsel or other representative, to such extent and upon such terms as may be deemed proper.
29 C.F.R. §102.29